Steerable interbody fusion cage

Abstract

An interbody vertebral cage facilitates minimally invasive approaches to the intervertebral disc for corrective restoration of disc height, stabilization between vertebra, and fusion. The preferred embodiment provides a streamlined, slender straight contour with a central hinge or other articulating apparatus that allows the introduction of the cage into the operative field and disc space in a minimally invasive, bone-sparing manner. After partial insertion, the hinge component is activated, allowing the operator to steer the cage anterior-medially within the disc space to an anterior-central position within the intervertebral space. In this state the cage is shaped like a crescent, chevron or boomerang.

I claim: 
     
       1. A method of fusing vertebrae, comprising the steps of:
 providing a steerable intervertebral cage comprising:
 a distal portion having front, back, top, bottom, inner and outer surfaces; 
 a proximal portion having a front, back, top, bottom, inner and outer surfaces, and 
 a hinge joining the front of the proximal portion to the back of the distal portion, such that the cage has a first, straightened shape with the hinge open and a second, crescent shape with the hinge closed; 
 
 introducing the cage in the first, straightened shape into an anterior central position within an intervertebral disc space using a posterior lumbar interbody fusion (PLIF) or transverse lumbar interbody fusion (TLIF) approach; 
 steering or allowing the cage to assume the second, crescent shape once within the intervertebral disc space; and wherein the method further includes the steps of:
 using a first instrument to maintain the cage in the straightened shape for introduction; and 
 switching to a different instrument that facilitates articulation and final positioning. 
 
 
     
     
       2. The method of  claim 1 , wherein the first instrument comprises a long-armed introducer, and wherein the different instrument comprises a second instrument comprising a short-armed introducer. 
     
     
       3. The method of  claim 2 , wherein the long-armed introducer comprises a long arm configured to engage the steerable intervertebral cage, wherein the short-armed introducer comprises a short arm configured to engage the steerable intervertebral cage, and wherein the short arm has a length less than the long arm. 
     
     
       4. The method of  claim 3 , wherein the long-armed introducer comprises a pair of arms configured to engage the steerable intervertebral cage on opposite sides of the steerable intervertebral cage. 
     
     
       5. The method of  claim 4 , wherein the short-armed introducer comprises a pair of arms configured to engage the steerable intervertebral cage on opposite sides of the steerable intervertebral cage. 
     
     
       6. The method of  claim 2 , wherein the long-armed introducer is configured to engage the steerable intervertebral cage along a greater portion of the steerable intervertebral cage than the short-armed introducer. 
     
     
       7. The method of  claim 1 , further comprising engaging the first instrument with a first longitudinal recess formed on the proximal portion of the steerable intervertebral cage and engaging the first instrument with a second longitudinal recess formed on the distal portion of the steerable intervertebral cage. 
     
     
       8. The method of  claim 7 , further comprising engaging the different instrument with the first longitudinal recess formed on the proximal portion of the steerable intervertebral cage. 
     
     
       9. The method of  claim 8 , further comprising closing the hinge such that the first longitudinal recess is aligned with the second longitudinal recess. 
     
     
       10. The method of  claim 9 , further comprising steering the steerable intervertebral cage through a curved path using the different instrument. 
     
     
       11. The method of  claim 10 , wherein the steerable intervertebral cage further comprises a stabilizing member configured to stabilize a hinging action of the hinge of the steerable intervertebral cage. 
     
     
       12. The method of  claim 11 , wherein the stabilizing member is positioned so as to couple the proximal portion of the steerable intervertebral cage with the distal portion of the steerable intervertebral cage. 
     
     
       13. The method of  claim 1 , wherein the steerable intervertebral cage comprises a symmetrical cage configured such that the symmetrical cage can be introduced into opposite sides of a patient's body by flipping the symmetrical cage over. 
     
     
       14. The method of  claim 1 , wherein the steerable intervertebral cage further comprises an anterior portion comprising a curved surface configured to facilitate penetration into the intervertebral disc space, and wherein the step of introducing the cage comprises introducing the cage into an anterior-central position within the intervertebral disc space with the anterior portion entering the intervertebral disc space first. 
     
     
       15. The method of  claim 14 , wherein the steerable intervertebral cage further comprises a posterior portion configured to engage with at least one of the first instrument and the different instrument. 
     
     
       16. The method of  claim 15 , wherein the posterior portion comprises a flat surface. 
     
     
       17. The method of  claim 16 , wherein the posterior portion comprises a threaded opening positioned within the flat surface. 
     
     
       18. The method of  claim 1 , wherein the proximal portion of the steerable intervertebral cage forms an angle with respect to the distal portion of the steerable intervertebral cage on the order of 40 degrees when the steerable intervertebral cage is in the straightened shape. 
     
     
       19. The method of  claim 1 , wherein the outer surface of the distal portion of the steerable intervertebral cage comprises a curved surface, and wherein the outer surface of the proximal portion of the steerable intervertebral cage comprises a curved surface. 
     
     
       20. The method of  claim 19 , wherein the steerable intervertebral cage is configured such that the curved surface of the distal portion and the curved surface of the proximal portion form a continuous outer curved surface in the crescent shape.